The present invention is directed to the removal of fine particles from gases. In particular the present invention facilitates the separation and collection of particulate matter, such as dust, mist, fumes, smoke, and also of noxious gases etc., dispersed in a gas, in a state of turbulent flow, by taking advantage of certain effects associated with turbulence in a novel and particular way, using purely mechanical means.
It is well known to those skilled in the art of fluid mechanics and related files of endeavour, that fine particles dispersed in a fluid in a turbulent state of flow tend to follow the eddies of the turbulent fluid.
The removal of very fine particles, typically in the range of about 0.01 to 100 microns, from industrial gases or ambient air, is a difficult and expensive operation to perform efficiently. Devices traditionally employed for this purpose involve electrostatic precipitators, a variety of filters, and wet scrubbers. Scrubbers are used also for the removal of noxious gases from industrial gases. Cyclone collectors have been traditionally used for the removal of particulate matter larger than about 5 microns, and a concerted effort has been made recently to extend their effective range down to about 1 micron particulate size.
In published International Patent Application WO93/15822 and corresponding U.S. application Ser. No. 08/290,883, filed Aug. 18, 1994, now abandoned, the disclosure of which is incorporated herein by reference, there is described a method for the removal of dispersed fine particulates from a fluid stream using the mixing effects of turbulence for the separation and collection of the fine particulates in a novel and specific way, by passing the fluid stream in a state of turbulent flow through a channel not containing any obstructions, alongside of which there is a region, freely communicating with the flow channel, in which the flow is hindered by a large number of objects or elements, placed close to each other in the flow path, causing a change from turbulent to viscous flow. Turbulent eddies, carrying particulates, keep penetrating into this region, which forms an expanded viscous sublayer, and deposit their particulate matter on the surfaces of the objects present there. Retention of the particulates on the surfaces is enhanced if the objects are charged with static electricity. Devices operating on the above principles of particulate collection from fluid streams will be referred to as "turbulent flow precipitators".
In accordance with the present invention, there are provided means for effecting such particulate separation, not disclosed in WO93/15822. In all embodiments the mechanism whereby dust is collected is the same, i.e. turbulent deposition by eddy penetration. All embodiments described here, and their future modifications, are based on this principle, and the patent applies to all. Some means of recovering or removing the collected dust are described here, but are by no means the only methods of removing collected dust from the system. Some are based on purely physical means (utilising, gravity), and some by mechanical means (such as louvred base, screw thread conveyor, conveyor belt, shaking mechanism, quick-returning shaking, etc.) Some embodiments are useful for small scale application (up to 500 acfm); some for mid-size (up to 5,000 acfm); and some may be modified for large industrial scale units; but all are based on the same underlying principle, that of turbulent deposition, as described here and in the patent application WO93/15822. Many of the embodiments can also be used, in addition to removing particulate matter, to eliminate noxious gases by means of either impregnating the collector surface with a suitable catalyst or an adsorbent such as active carbon, or by using a fine spray of water or suitable aqueous solution and injection of that into the turbulent gas stream, ahead of the collector device. In the first instance, the eddies keep transporting the noxious gas to the collector surface, where it reacts or gets adsorbed. In the second instance, the fine spray, after absorbing the noxious gas, is precipitated by turbulent deposition. In this case the turbulent flow precipitator is acting as a wet scrubber. Dry scrubbing is another field of application of the turbulent flow precipitator, where it can be used to collect dry particulates formed in the process. Some of the further means of particulate collection are described below with reference to the accompanying drawings, in which: